Which one of the following bacteria has the potential for nitrogen fixation?

$A$: Bacteria enter only the polyploid cells of the root cortex.
$R$: These cells provide cytokinins to bacteria,which promote bacterial cell division.

The $hup$ gene is found in .........

Which of the following is responsible for nitrogen fixation in an aquatic fern?

Select the correct statements from the given:
$(a)$ Nitrogenase is a heterodimeric protein.
$(b)$ Root hairs curl by action of nitrogenase and plant 'nod factors'.
$(c)$ During symbiotic $N_2$ fixation,$ATP$ is provided by the legume plant.

Which plant tissue of the root is responsible for the formation of root nodules in plants of the family $Fabaceae$?